Field of the Invention
The present invention concerns a method in order to generate an RF excitation pulse with which an arbitrarily shaped volume can excited for obtaining magnetic resonance (MR) signals. Moreover, the present invention concerns a method with which only the nuclear spins within a predetermined vessel can be specifically excited. The present invention also concerns a method in order to create MR angiography images with the use of the initial methods, as well as corresponding magnetic resonance systems to execute the method according to the invention.
Description of the Prior Art
In vascular-specific MR angiography, and in MR perfusion measurements, the nuclear spins in one or more blood vessels (in particular arteries) are specifically excited or saturated, which is also designated as “labeling”. The movement of these spins due to flow or perfusion within the tissue can subsequently be tracked. For this purpose, the excitation volume that is excited by the RF excitation pulse is selected so that only the vessel of interest (and no other vessel) lies within the excitation volume. Ideally, the RF excitation pulse is selected such that it excites only the vessel of interest (and not the areas around the area of interest). For this purpose, according to the prior art selective RF excitation pulses are used, for which excitation with multiple RF antennas can be advantageous.
In “Selective Labeling of Moving Spins using Parallel 3D Spatially Selective Excitation”, J. T. Schneider et al., Proc. Intl. Soc. Reson. Med. 20, 2012, Page 640, it is described how the spins in a vessel in three-dimensional space can be specifically excited with multiple RF antennas.
According to the prior art, the following two objects must be achieved for targeted excitation of a vessel:                The spatial position and the spatial dimensions of the vessel must be determined.        An RF excitation pulse must be calculated which excites only the spins within the vessel.        